San Francisco Chronicle: Amid growing concern over an imminent shutdown of the commercial and sport chinook salmon season, scientists are struggling to figure out why the largest run on the West Coast hit rock bottom and what Californians can do to bring it back. The chinook salmon – born in the rivers, growing in the bay and ocean, and returning to home rivers to spawn – need two essential conditions early in life to prosper: safe passage through the rivers to the bay and lots of seafood to eat once they …